It is known in modern motor vehicles to provide a fuel system that includes a fuel filler pipe through which the fuel tank can be filled with liquid fuel such as gasoline or ethanol. The vehicle is refueled by inserting a service station nozzle into the funnel of the fuel filler pipe and then pumping the liquid fuel down the fuel filler pipe to the tank.
In order to limit the expulsion of fuel vapor into the atmosphere, modern vehicles are equipped with onboard vapor recovery systems, one element of which is a vapor recirculation pipe that extends between the fuel filler pipe and the fuel tank. The vapor recirculation pipe is intended to recirculate fuel vapors between the fuel tank and the funnel region of the fuel filler pipe. However, during the filling of the tank, conditions can occur in which liquid fuel is splashed into the vapor recirculation pipe, for example in the event of a malfunction of the service station nozzle, or an operating error by the person filling the tank.
Accordingly, the prior art has employed an orifice-like plug that is positioned within the recirculation pipe to allowing a metered volume of fuel vapor flow but limit fuel liquid flow.